The Negative Stiffness Device (NSD) is a device that produces a force which is in the same direction as the imposed displacement thus the name “negative stiffness”. The NSD consists of (a) a highly compressed spring that produces the negative stiffness, (b) a magnification mechanism to magnify the negative stiffness, (c) a self-containment system so that the large forces needed for developing the negative stiffness are not resisted by the structure, and (d) a "gap spring assembly" (GSA) mechanism which delays the development of negative stiffness until the structural system undergoes a prescribed displacement. The prototype of the negative stiffness device was designed by researchers at the University at Buffalo (UB), Rice University and Taylor Devices Inc., built at Taylor Devices Inc., and was first tested on a shake table by researchers at UB and Rice University in a three stories structural model isolated with elastomeric bearings.